Eternal Monuments Among the Stars

by Paul Gilster on January 24, 2012

Yesterday’s post looked at SETI and its assumptions, using the lens of a new paper on how the discipline might be enlarged. The paper’s authors, Robert Bradbury, Milan Ćirković and George Dvorsky, are not looking to supplant older SETI methods, but rather to broaden their scope by bringing into play what we are learning about astrobiology and artificial intelligence. It is perilous, obviously, to speculate on how an alien civilization might behave, yet to some extent we’re forced to do it in choosing SETI targets, and that being the case, why not add into the mix methods that go beyond our current radio and optical searches, methods that may have a better chance of success?

The Engima of Contact

A key to extending SETI’s reach is to question the very idea of contact. One assumption many of SETI’s pioneers had in common was that there was an inherent need to communicate with other species, and that this need would take the form of intentional radio beacons or optical messages. What Bradbury, Ćirković and Dvorsky are calling ‘Dysonian SETI’ makes no such assumption, and actually gains strength from the fact that it does not. Acknowledging that we have not yet found an undisputed detection signature, Dysonian SETI says that intention is not necessary. A civilization may be detectable through its artifacts. A Dyson sphere, for example, should show an infrared signature that is distinguishable from the normal spectra of stars.

Once in place, a Dyson shell should be durable enough to potentially outlive its creators, ‘Ingrafted in eternal monuments/Of Glory,’ to cite the verses from Lucretius the authors use to illustrate their point. Thus we get around a significant problem noted by many SETI writers — the ‘window of opportunity’ for radio SETI is short, a mere flicker in the span of our own civilization, much less the span of our planet’s existence. Even if you posit a stunningly optimistic figure of 106 technologically advanced civilizations in the galaxy, it is clear that these cultures will exist at different levels of development. What are the odds that two will be at precisely that stage of technical evolution to enable back and forth radio communications?

Image: NGC 6744, a spiral galaxy some 30 million light-years away in the southern constellation of Pavo (The Peacock), as captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope. If tens of thousands of civilizations co-exist in such a galaxy, how many will be close enough to each other in terms of technological development to make radio or optical contact likely? Credit: ESO.

Dysonian SETI would surmount this problem because enormous astro-engineering projects could exist as archaeological survivals no matter what the fate of their parent civilization. The idea seems plausible and does not foreclose the ongoing SETI effort in radio and optical wavelengths. But the authors point out that our assumptions about artifacts themselves also need to be adjusted. If civilizations move toward a ‘singularity’ in which artificial intelligence leads to a kind of postbiological evolution, then searching for Dyson spheres takes a twist.

Why? Because so far we have assumed a Dyson shell roughly the size of Earth’s orbit, one with a working temperature that would sustain our kind of biological life on the surface of the shell. These parameters hardly fit the needs of postbiological intelligence. From the paper:

…from a postbiological perspective, this looks to be quite wasteful, since computers operating at room temperature (or somewhat lower) are limited by a higher kT ln 2 Brillouin limit, compared to those in contact with heat reservoir on lower temperature T…

I think what the authors are referring to above is also called the Landauer limit, which defines the minimum amount of energy needed to alter one bit of information — here k is the Boltzmann constant while T is the temperature of the circuit (K) and ln 2 is the natural log of 2. In any case, cooler is better. The paper continues:

Although it is not realistic to expect that efficiency can be increased by cooling to the cosmological limit of 3 K in the realistic model of the Galaxy, still it is considerable difference in practical observational terms whether one expects a Dyson shell to be close to a blackbody at 50 K, as contrasted to a blackbody at 300 K. This lowering of the external shell temperature is also in agreement with the study of Badescu and Cathcart… on the efficiency of extracting work from the stellar radiation energy. In this sense, the Dysonian approach needs to be even more radical than the published intuitions of Dyson himself.

Beyond the Dyson Shell

Widening the theoretical background of ongoing searches (the authors point to SETI@Home as one example of widely distributed processing) means taking such new perspectives into consideration, and the paper goes on to flag other possible signatures of an extraterrestrial civilization:

Unusual chemical signatures in stellar spectra, which could indicate a technological culture trying to be noticed by distant astronomers

Gamma-ray signatures created by antimatter burning in the activities of an extraterrestrial civilization

Recognizable transits of large artificial objects

Analysis of extragalactic astronomical data, which could reveal the presence of large-scale structures and Kardashev Type III astro-engineering

Interestingly enough, all of the above have been the subject of initial studies, and the bibliography of the paper (see yesterday’s citation) is laden with these and other references. These investigations have been regarded as little more than curiosities, but the impact of the discovery of clearly artificial objects would have such a quickening effect on human self-awareness that they are clearly worth the limited funds thus far spent on them.

Widening the Search Space

A Dysonian SETI would evolve along the lines suggested by Freeman Dyson himself when discussing the supposed willingness of alien civilizations to communicate with each other, and their implied benevolence when it comes to greeting new members to the ‘galactic club.’ Dyson would have none of it, saying “…I do not wish to presume any spirit of benevolence or community of interest among alien societies.” Why indeed do so, when a search for Dysonian artifacts like Dyson shells would make no such assumptions, while allowing us to bring to bear what we are learning about nanotechnology, artificial intelligence and astrobiology?

Why not widen the search space, then, adding to the already impressive and groundbreaking work of SETI’s pioneers by bringing into play recent findings like those of Charles Lineweaver, whose work shows that Earth-like planets in the habitable zone of the galaxy (itself a relatively new concept) are on average 1.8 billion years older than our planet? Assume civilizations not just millions but potentially a billion or more years older than our own and you play down the importance of contact (it is hard to imagine the advantages of such to the alien culture) but leave open the prospect of discovering the works they have built and possibly left behind.

Let me close with another quote from this vigorous paper re SETI old and new:

…the two approaches are at present compatible and should be pursued in parallel at least until there is better theoretical insight into the preconditions for emergence of technological civilizations in the Galaxy. The ability to extract information from the interstellar environment increases dramatically with each passing year. As the resolution of the data increases, so does the ability to process and infer its nature. This process will deeply challenge conceptions of the Universe and what we think we know about it. It will also challenge the way in which we see ourselves and our potential as an intelligent civilization.

philw1776 – The only reason we haven’t found alien life yet is because we have not seriously searched for it, plus we have not even been at it for even one century yet, and in a galaxy 10 billion years old no less.

Most SETI programs have been sporadic or only sifting through a few kinds of frequencies. The same for looking for distant alien artifacts or scanning other galaxies. METI programs have happened even less, with most of them being conducted almost as acts of rebellion.

We have sent just TWO missions to another world to deliberately look for life and that was in 1976 when we did not fully understand the environment we were searching in. Yes we examined lunar rocks for life forms but few seriously expected us to find organisms on the Moon.

I have said elsewhere that the smoking guns of life beyond Earth are more than just helpful hints, while still saying I know they are absolute proof of life. This is also why I do not consider my view that there is life elsewhere to be an act of faith, because faith in something often does not require any evidence for it and sometimes even revels in a lack of solid evidence.

I have also said elsewhere that a strong declaration of the non-existence of alien life based on our early and immature findings has the strong scent of religious and political motivations behind it. When we start getting mature and serious about exploring the galaxy and not finding alien life, then we can become more definitive.

Nick, I think that you missed that your Tolkien Paradox just speaks to a meta-analysis of the premises. Fermi’s friends really were trying to convince him of the wonders in store for us if we could contact other ETI’s in the galaxy, and the worthiness of expending effort to that effect. Very practical.

Since the laws of physics are universal, if life can arise once it can arise twice (and more). The question then becomes one of determining the probability of abiogenesis given a set of conditions, and the probability of those conditions occurring.

Calculating those probabilities is difficult. Guesses aren’t interesting or useful. There is no easy way to constrain the probability range for abiogenesis from first principles. Therefore we try for statistical sampling, which is being done. These programs include astronomical searches for bio-signatures and SETI. Both are challenging and problematic (more so in the SETI case) since you can never know when to give up unless you actually do find something. Even the null results of experiments on Mars are not conclusive of no life now or in the past.

Avatar, self-replication of molecules is much simpler than you think. Replicating molecules with high information content, such as some clays are also reasonably common. Unfortunately modern synthesis (aka neoDarwinian theory) requires a much higher connection of that information with reproductive success and a much higher fidelity of intergenerational transmittance of information than seems feasible in any simple model. Under all other conditions evolution would look as if it acts in reverse and deconstructs any well tuned system (especially if it is complex). Thus that problem is more complex than you express.

I am however pleased that Nick highlights the often neglected problem that most imaginable nascent life-forms will die for the slow synthesis of at least one nutrient within their new closed ecosystem. That in itself does not quite lead to a problem that is many orders of magnitude in depth as some others in abiogenesis (to me its hard to see more than 99% of fresh cases of abiogenesis starving themselves to death) but I sometimes wonder: would any ecosystem thrive sufficiently to give interesting results. There really may be something to Lovelock’s Gaia, and then, again, there might not.

@Eniac
“Right, because that is not possible. However, the Fermi paradox is based only on a very general assumption: There is a possibility that an intelligent civilization can spread among the stars. No models or predictions of any sort are called for. All that is needed is the possibility of self-replication of “life” (original or artificial) across interstellar distances. Autonomous self replication implies expansion into all available living space. Bacteria do it, trees do it, people do it too. If you know of a mechanism by which this rule could be broken, or an example of it being broken in experience, please name it.”

I would never confuse bacteria and trees with an advanced technological civilization.
Even Sociocultural evolution predicts the ‘singularity’, beyond which we don’t understand anything. I do not subscribe to this Singularity thing.
Still it shows that one cannot use Biological Evolution to make definitive predictions about the future of a highly developed global technological society.
(If the one know survives!)
Many confuse biological evolution with SocioCultural Evolution.
We are in a situation never seen before in the Earth’s history.

I should have added that Nicks starving ecosystem hypothesis would work well in destroying any ideas that natural forces can gradually (over millions of years) bring a primordial soup up to a complexity where life will spontaneously form from it. But does anyone prominent still believe that particular path to abiogenesis possible?

I have said elsewhere that the smoking guns of life beyond Earth are more than just helpful hints, while still saying I know they are absolute proof of life. This is also why I do not consider my view that there is life elsewhere to be an act of faith, because faith in something often does not require any evidence for it and sometimes even revels in a lack of solid evidence.

Those guns you refer to (plenty of suitable conditions for life, I suppose?) are not smoking. They may be there, but we have no idea if they were ever loaded. Evidence for preconditions of an event is not evidence of the event itself. There is a profound lack of evidence for actual ET life in which your faith can revel.

In order to come into being, this simplest molecule requires hundreds of chemical steps to occur in just the right order

This is an assertion without evidence. We do not know enough about what kinds of self-replicating molecules, or how many different kinds there could be, to even begin considering probabilities at all.

which is insanely improbable.

If it is so improbable that it would only happen once per trillion worlds per 10 billion years, then it is more than probable enough to explain life on earth and hypothesize a universe teeming with many other examples of life.

It is not “insanely” improbable. Rather, it is, most definitely “sanely” improbable.

The only thing we can say for certain with what we know is this: we are here. And since we most definitely descend from a self-replicating molecule, by whatever process, unguided or not, by which it happened, we know, with absolute, undeniable certainty, that the probability of such an event happening is at least 1 per universe per 14 billion years.

I am however pleased that Nick highlights the often neglected problem that most imaginable nascent life-forms will die for the slow synthesis of at least one nutrient within their new closed ecosystem.

Only if it runs out of that hypothetical nutrient before successfully diversifying into an ecosystem (something which evolutionary theory has demonstrated will happen automatically, given sufficient time).

So the only problem is finding an environment or set of circumstances wherein the necessary nutrients are in sufficient abundance (or recycled by abiotic geologic mechanisms) to sustain the first self-replicator long enough.

And since we have no idea how long is long enough, and abundant is abundant enough, or what kinds of nutrients we are talking about, we cannot say, except as wild-assed guessing, anything intelligible whatsoever about whether or not this is a problem, or how big a problem it might be.

In my previous post, I spoke ‘of the simplest molecule that can replicate itself even halfway reliably (I’m NOT talking about the simplest cell, etc).’

Why did I choose this simplest molecule and not the simplest cell?
Because, if you have a molecule that can replicate itself somewhat reliably, darwinian evolution takes over – AKA the molecule that replicates best produces more copies of itself, having a HUGE advantage.
But, before you have said molecule, you have no darwinian evolution – a trait that could lead after 50 further chemical steps to the self-replicating molecule has no advantage whatsoever over useless traits. At this stage in the game, you have only probability.

What do we know about abiogenesis?
After decades of research, not much – speculations, mostly.

You mentioned crystals/clay as the replicating substrate (clay hypothesis). It was experimentally shown that crystals cannot replicate reliably enough:http://www.rsc.org/Publishing/ChemScience/Volume/2007/08/Crystals_as_genes.asp
We could, of course, speculate that a rather complex molecule in conjunction with the clay could lead to reliable self-replication – but we’re back where we started – the complexity needed for a self-replicating molecule.

The RNA world hypothesis is popular and well-researched – and the scientists working at it hit this problem regarding the complexity a reliably self-replicating molecule needs to have – and failed to resolve it. See Gerald (Jerry) Joyce and Leslie Orgel and their “magic catalyst” that can generate such a molecule.

So – what do we know?
That NOT ‘all roads lead to Rome’. If it were so, life would have been created in a laboratory long ago.
That life – or a self-replicating molecule – cannot be crated in ~10 easy steps. Again, if it were so, life would have been created in a laboratory long ago.

What are the chances of abiogenesis, then?
As said, in order to obtain a reliably self-replicating molecule (in a lab or elsewhere), you need to traverse a lot of chemical steps in just the right order.
Let’s assume the number of chemical steps needed is 100 (a conservative estimate).
The chance of all these chemical steps occuring in nature in just the right order is 100 factorial = 1 chance in ~9×10^157. This is ENORMOUSLY improbable.
For a comparison, the number of atoms in the observable universe is only 10^80 and the age of the universe is only 4.3×10^17.
The conclusion would be that, probabilistically speaking, life appeared only once in the observable universe + a HUGE chunk of the unobservable universe. Of course, my factorial is an oversimplification (it does not take into account a multitude of elements) and should be taken as such – it’s only meant to give a starting point.

Note that even if the true answer regarding the probability of abiogenesis is 130 orders of magnitude more favourable than my factorial example, it is overwhelmingly likely (practically a certainty) that we are the only life in the local cluster of galaxies.

And, of course, I have not even taken into account the additional difficulties Nick has mentioned.

In conclusion, as I said, this improbability of abiogenesis explains beautifully why there’s no other life in the neighbouring ~trillion galaxies.

Bob
“Avatar2.0, I have to disagree with your assessment. Both Occam’s razor and the improbability of life arguments rest on unprovable assumptions on our part based on our ignorance of nature.”

About the improbability of biogenesis – see my above post.
About the Fermi paraxdox explanations that break Occam’s razor – vaious posters already explained how various explanations involving abundant life throughout the universe break Occam’s razor.

For example, in the ‘Rethinking SETI’s Targets’ thread, Rob Henry debunked (aka showed that it breaks Occam’s razor) the ideea that ETIs exist, but all of them stay at home ‘just because’ (cultural/religious/etc reasons):
‘I’ve notice that about half of all commenters here seem to hold 3 implicit assumptions.
1) All ETI’s have very similar characteristics to each other but not necessarily to us.
2) All ETI civilisations lack internal variation derived by the individualistic thinking that is characteristic of our society
3) All ETI civilisations hold their current outlook for billions of years.’

In this very thread, Nick debunked the ideea that ETI civilizations stay quiet and hidden to avoid predatory ones:
‘The dominant organization in a galaxy doesn’t need to hide from anybody. Furthermore, wars are at least as likely to produce very high energy, very visible outputs as stealthy ones. If this occurs in even a few out of the hundreds of billions of known galaxies, we will likely soon see it.
Struggle produces competing imperatives. Plants would love to hide from herbivores, but they can’t, because they have an even more important need for sunlight, and thus pursue the Malthus/Darwin imperative of capturing as much sunlight as they can. As a result our planet produces very distinctive and large-scale emission and reflection spectra. An advanced civilization will similarly need large surfaces to capture and radiate energy, following the Malthus/Darwin imperative to use as much power as possible, and many of them will also benefit from illuminating these surfaces in order to work or play around them or to try to capture each others’ attention.’

“I could as well argue that if life emerges anywhere in the galaxy, known mechanisms allow at least microbial life to propagate through space and potentially be able to seed every hospitable world in the galaxy in only a few tens or hundreds of millions of years. That would allow similar DNA based life to begin to evolve on countless worlds.”

Interplanetary panspermia – plausible.

Innterstellar panspermia? Not even in the general vicinity of ‘plausible’; more like in the vicinity of ‘practically impossible’.
Unless you have intelligence – then it becomes extremely probable, in the fullness of time.

Why is interstellar panspermia so ridiculously improbable?
Because the distances between star systems are so large, the human mind can only process them as mathematical abstractions.
After an impact, a meteorite, carrying life on it (microbes which survived the impact), could excape its planet. But the chances that this meteorite has the exact trajectory to reach not only another star, but a planet around said star are beyond minuscule.

[Quoting LJK] I have said elsewhere that the smoking guns of life beyond Earth are more than just helpful hints, while still saying I know they are [NOT] absolute proof of life. This is also why I do not consider my view that there is life elsewhere to be an act of [religious style] faith, because faith in something often does not require any evidence for it and sometimes even revels in a lack of solid evidence.

“Those guns you refer to (plenty of suitable conditions for life, I suppose?) are not smoking. They may be there, but we have no idea if they were ever loaded. Evidence for preconditions of an event is not evidence of the event itself. There is a profound lack of evidence for actual ET life in which your faith can revel.”

LJK replies:

Referring to the term “smoking gun”, one type of those very examples, the hydrothermal vents found on the ocean floors which support an ecosystem of giant clams, weird spider-like crabs, and red-and-white tube worms, are referred to as “black smokers” – so there. :^)

For the record, before the hydrothermal vents were discovered in 1977 with their alienish dependent organisms, most scientists thought the ocean bottoms were largely devoid of life. They based this in part on the facts that sea floors were very cold, very dark due to lack of sunlight, and the crushing pressures caused by having miles of ocean water on top of them.

Scientists had conducted a few expeditions to small sections of the ocean floors but found little in terms of life. For example, the first submarine to reach the deepest place on Earth, the Trieste expedition of 1960 to the Mariannas Trench in the Pacific, stayed at the very bottom for only a few minutes. The two crewmen could see almost nothing out their little window as their vessel had stirred up the sea floor sediment, clouding the surrounding environment. The focus of the mission was more about setting a record and testing submarine equipment than conducting marine biology, anyway.

Then the vents were found 17 years later and these assumptions went out the window. A similar comparison can be made to the status of our explorations of space and the Universe.

If we were unable to ascertain the true state of life in our deep oceans until just a few decades ago (and there is still so much we have yet to learn about the other 75% of Earth’s surface), then is it not just a bit premature to declare the incredibly vaster galaxy and beyond to be deserts lacking life?

Of the few thousand exoplanets we know about, we can only see directly a mere handful, and they are just blips of light. We have examined a few worlds with other methods to determine such things as the compositions of their atmospheres, but this too is paltry in terms of what of else needs to be known about all these alien places – and the several hundred billion that are estimated to swarm throughout the Milky Way.

Reexamine how much serious scientific exploration we have conducted in the last century for both our planet and our Universe and you will see that we are not as far along as we like to think, especially when it comes to the search for alien life.

So I say again, it is too early to conclude if Earth life is unique or not and we MUST ramp up our searches for it with as many scientific methods as possible.

I don’t think that a lack of discovery of intelligent extraterrestrial activity refutes the assumption that life is common in the galaxy. There may be a simple reason why SETI has been fruitless so far: the inverse square law. ETIs wouldn’t be able to pick up our radio or TV signals even at a distance of “only” 1 or 2 light years out. Even powerful search radars would only be detectable by telescopes operating on planets orbiting stars in the immediate vicinity of our own solar system.

Even extremely energy intensive activity by ETIs can only be detected at a limited range.

According to a Zubrin paper, the Hubble space telescope could detect a 1,000,000 tonne (huge!) antimatter-driven starship accelerating away, if its exhaust were pointed directly at us, at a distance of a few hundred light years. And that’s as good as it gets. We would need to build much larger telescopes to detect (similarily huge) fusion engines or magsails operating at similar distances.

So basically we are not able to detect any ETI which is not deliberately contacting us, unless its a Kardashev III, manipulating stars in an “unnatural” fashion.

Regarding abiogenesis: life appeared as soon as the conditions for its survival became right on Earth. This is evidence that the probability of abiogenesis is high, rather than low. I’m hopeful that we’ll find evidence of life on Europa and perhaps Mars as well, if governments and space agencies get their acts together and start funding real missions to these places (Mars sample return and a Europa submarine would be great).

I also question a core assumption of the Fermi Paradox: extraterrestrial civilisations colonise neighbouring star systems and thus spread across the entire galaxy within a few million years.

Say we discover planets around A-Centauri A and B, all of them “dead rocks”. Why would we “colonise” such a system?

The nearest Earth-like (not life-bearing but Earth-like) planet may be hundreds if not thousands of light years away … too far away for any attempt at settlement unless we find a way to bend the laws of physics.

I have to disagree with Avatar2.0’s comments on the extreme rarity of life in the universe.

Avatar2.0’s reasoning is as follows: “you need to traverse a lot of chemical steps in just the right order. Let’s assume the number of chemical steps needed is 100 (a conservative estimate). The chance of all these chemical steps occuring in nature in just the right order is 100 factorial = 1 chance in ~9×10^157. This is ENORMOUSLY improbable.”

This reasoning disregards two facts. The first is that the number of chemical steps in your factorial example is not actually sequential. A self-replicating molecule isn’t assembled atom-by-atom, it is built from a set of slightly less complex molecules which in turn come from a slightly less complex group of molecules, etc. This reduces the odds of occurrence in nature dramatically and is not the type of process that can be modeled by a simple “factorial” argument. The second point is that self-replicating molecules DID arise on the Earth almost as soon as the planet cooled down enough (following its formation) that the remaining heat could not break the molecular bonds. That’s real empirical evidence that suggests that life can and will form almost anywhere where the conditions are favorable.

The energy costs of interstellar colonisation vs expanding living space in the home system simply don’t add up: crossing interstellar space at 0.1c and setting up a colony on another world would cost roughly 10^8 times as much energy as creating the same amount of living space in the home system in form of a o’Neill habitat.

“Colonisation of the home planetary system is rational, colonisation of the stars is irrational”.

Highly advanced civilisations have to be rational, otherwise they wouldn’t have reached that state of development.

“Why is interstellar panspermia so ridiculously improbable?
Because the distances between star systems are so large, the human mind can only process them as mathematical abstractions.”

If one considers that the actual extent of the possible life bearing sphere of debris, comets and uncountable dust grains which may surround a stellar system might be up to a good fraction of a light year in extent, then consider the fact that many stars are actually closer together than in our region of the galaxy, one can appreciate how these “spheres of influence” could easily interact.

Life bearing but dormant interstellar grains might need to only get within this sphere to interact with one of the perhaps trillions of comets which ultimately may allow that life to replicate and seed the entire sphere in time.
Then other processes may sweep some of those grains out again to repeat the process.

I would argue that the “life sphere” around any star may be on the order of perhaps 50,000 AU. That makes stellar systems fairly large targets in my view.

I admit that these are my mere speculations, but I would appreciate it if anyone with knowledge of actual simulations on the matter would chime in.

Because the distances between star systems are so large, the human mind can only process them as mathematical abstractions.

After an impact, a meteorite, carrying life on it (microbes which survived the impact), could excape its planet. But the chances that this meteorite has the exact trajectory to reach not only another star, but a planet around said star are beyond minuscule.

LJK replies:

The odds of a substantial chunk of one planet being naturally able to go from one solar system to another across interstellar space and land on a particular world are indeed quite small.

However, one form of material that can spread across the galaxy and land on many worlds is interstellar dust grains. Every solar system produces them in huge abundance and the solar wind and other forces push them out into deep space. We have found them in our Sol system.

Some have speculated that microbes could ride on those dust grains and transplant themselves onto viable worlds. Even if they do not survive the journey alive, their organic material could provide the catalyst to develop life on other worlds.

Amphiox and avatar are trying to work out whether abiogenesis is insanely improbable or sanely improbable, and I think that that captures the whole topic entirely.

If we await statistically random events to construct something of high complexity, we can expect our wait to be million of orders of magnitude of years. If we can expect our natural construct to be merely due to a congruence of a few rare conditions in a confined space, a wait of just a few million years would be more typical.

I put it to you both, that as yet, we do not know which of these two situations we are facing. Each of these speculation has its strong points, but they also enable a situation where it is easy to talk past each other to the detriment of both parties.

Scott G.
“I have to disagree with Avatar2.0′s comments on the extreme rarity of life in the universe.

Avatar2.0′s reasoning is as follows: “you need to traverse a lot of chemical steps in just the right order. Let’s assume the number of chemical steps needed is 100 (a conservative estimate). The chance of all these chemical steps occuring in nature in just the right order is 100 factorial = 1 chance in ~9×10^157. This is ENORMOUSLY improbable.”

This reasoning disregards two facts. The first is that the number of chemical steps in your factorial example is not actually sequential. A self-replicating molecule isn’t assembled atom-by-atom, it is built from a set of slightly less complex molecules which in turn come from a slightly less complex group of molecules, etc.”
As in the slightly less complex molecules undergo a chemical step to become more complex, repeat, repeat.
This is my exact description, Scott G. (I conservatively chose the number of these chemical steps to be 100 – after which, we have a molecule complex/ordered enough to actually be able to self-replicate ~reliably). The fact that the dice are thrown more than once, at the same time, in the same warm pond/hot vent/etc changes nothing.

I never said the self-replicating molecule needs to be assembled atom by atom – do read my previous post.

“This reduces the odds of occurrence in nature dramatically and is not the type of process that can be modeled by a simple “factorial” argument.”
Why not, exactly, Scott G.?
My factorial argument does ignore a multitude of factors (for example, it ignores the fact that millions of environments were possible on early Earth, not just 100) – but applicable it is.

“The second point is that self-replicating molecules DID arise on the Earth almost as soon as the planet cooled down enough (following its formation) that the remaining heat could not break the molecular bonds. That’s real empirical evidence that suggests that life can and will form almost anywhere where the conditions are favorable.”

To take as example our solar system:
For interstellar panspermia, the dust/meteorites must contain microbes. And there is – relatively speaking – little such dust/meteorites being generated by Earth.
The vast majority of this dust/meteorites doesn’t have the velocity needed to escape the solar system.
The dust/meteorites that does have the necessary velocity is not targeted at Alpha Centauri. The probability of ANY of it reaching a planet around Alpha Centauri, 4 ly out, is, as said, extremely small.

About meteorites/dust:
Microbes are unlikely to survive being hurtled into space.The ones that survive are less likely to be alive in dust/meteorites which have solar escape velocity (the impact which hurtled them into space being more severe) as opposed to slower dust/meteorites.
Microbes are generally less likely to survive inside/near dust than inside meteorites (which are far fewer than the grains of dust).
Microbes are unlikely to survive the millions/tens of millions of years a journey to the nearest star would take – cosmic rays, radiation, etc.
And, at the end of their journey, microbes are unlikely to survive the impact with the destination planet. If they do, they are really unlikely to encounter a planet which can support them multiplying.

Even if Earth were to be turned to dust – all of which has the velocity to escape the Sun’s gravitational pull – and this dust was fired blindly in all directions into space, the probability of any grain of this dust reaching a planet arounnd Alpha Centauri, 4ly out, remains very small. 4 ly is just so IMMENSE a distance.

If two suns are closer than 4 ly, the chance of interstellar panspermia increases, indeed – between those stars only.
But there is a long distance from this to:
“I could as well argue that if life emerges anywhere in the galaxy, known mechanisms allow at least microbial life to propagate through space and potentially be able to seed every hospitable world in the galaxy in only a few tens or hundreds of millions of years.”

Bob, Fred Hoyle’s version of panspermia (which is what you seem to be referring to) is wonderful in its concept and detail. The space available here disallows me from systematically outlining its many strengths and weaknesses but I will make the following points.

It does not follow on from lithopanspermia, since any life trapped within the pore-space of rock would suffer lethal radiation from its natural radionuclides, and from secondaries generated from cosmic rays, on an interstellar timescale. This is not a problem for times scales typical for transfer between planets.

It is a natural follow on from Arrhenius’ radiopanspermia, but skirts some of the worst failings of that theory. Hoyle requires implantation of new bacteria into a system so very early that at least a couple of mechanisms are available to liquefy the interiors of some large comets.

His theory is highly testable, since either he is wrong, or life is ubiquitous in our galaxy and solar system. An example of this is that he predicts testable levels of stratospheric bacteria, some of which are not found alive anywhere else on Earth.

After reading Avatar’s reply to Bob’s question I feel that I should weaver it together with my previous post on the matter by adding the following comments.

Avatar shows why interstellar versions of panspermia need a huge production of spores to remain viable as models. Hoyle can only provide that if the Oort clouds of most living systems go through a phase in which a reasonable fraction of the mass of some comet is converted into bacterial spores, and if one such comet is involved in passing on the infection in earlier cycles, most (later) systems will have most of their comets infected by such bacteria. If Hoyle is right bacterial spores are most likely everywhere.

Also, the point I was making about early life on Earth is not to say that because there is life on Earth, there must be life everywhere; it is to say that the fact the life arose on the Earth almost as early as it COULD, tells us something. If life were inherently improbable, then it wouldn’t have started on Earth more-or-less the instant it stopped being pummeled by asteroids.

As I understand it, it is an accepted view that cometary and interstellar dust grains are constantly reigning down on the earth. If not, why would NASA spent real money to retrieve and study them?

“And, at the end of their journey, microbes are unlikely to survive the impact with the destination planet.”

The amount of dust that falls on earth is more like a gentle rain which amount to 40 tons per year. NASA’s STARDUST probe found no evidence yet of actual microbes but they did find an amino acid in the dust which was proven not to be contamination.

Life bearing but dormant interstellar grains might need to only get within this sphere to interact with one of the perhaps trillions of comets which ultimately may allow that life to replicate and seed the entire sphere in time.

You are supposing that germs would not only remain viable in the near absolute zero temperatures so far from the sun, but that they would also be able to replicate and spread under those conditions. With all due respect, I find that preposterous.

Scott G:

The second point is that self-replicating molecules DID arise on the Earth almost as soon as the planet cooled down enough (following its formation) that the remaining heat could not break the molecular bonds. That’s real empirical evidence that suggests that life can and will form almost anywhere where the conditions are favorable.

Even if they do not survive the journey alive, their organic material could provide the catalyst to develop life on other worlds.

What? Not surviving means being dead, unable to procreate. Do you seriously think that the remains of a dead organism will do anything other than quickly disintegrate without a trace when dropped on a chemically active world?

Max:

Say we discover planets around A-Centauri A and B, all of them “dead rocks”. Why would we “colonise” such a system?

Not in a heartbeat, or even in a hundred years. But eventually, for sure. Generally, the way it would most likely work is colonization first from the home planet to interplanetary space, and then, much later, as the solar system becomes ever more crowded with habitats and interstellar propulsion becomes ever more affordable, at some point a tiny faction in a humongous society may decide that the completely unoccupied system next door, i.e. a mere 4 ly away, beckons too much to be passed up, with completely unspoiled resources in its asteroid belt(s) and wide open living space around its sun(s). None of that pesky government prescribing proper orbits, putting planets off limits, collecting taxes, and other such nonsense. And perhaps, even a planet or two in the HZ to orbit around, for the scenery…

Note that it does not really matter whether these are the original biological organisms, or their artificially created descendents, or even completely transcendent entities. As long as they still procreate and require space and resources, they will want to move on eventually.

Rob Henry wrote: The real core assumption is that “not every subsection of society within every EII civilisation will be against stellar colonisation throughout their entire history”

In my view, a society capable of launching significant masses at significant fractions of light speed across interstellar distances has to be a highly rational society, otherwise it wouldn’t have advanced to this point.

Even today we don’t see people lining up to colonise Antarctica, or the sea floor. Throughout history, the underlying drivers of colonisation which led to lasting settlement have always been economic concerns. As Drake has shown, there will never be an economic imperative for interstellar colonisation.

The closest habitable planet may be a good 50 ly away. Ships would have to travel at at least 50% c in order to make the trip within a single human lifetime (assuming a generous rise in average life expectancy). The energy requirements for such a mission would be staggering.

To accelerate a 120,000 ton colony ship with a 200km diameter “sapphire” laser light sail (half of the mass would be the sail) to 50% c, the laser, with a 50km aperture, would need to produce a beam with a power of roughly 65,000 TW and it would need to maintain that output over a period of 1380 days. This amounts to a little more than 2 Billion Terawatt hours of energy consumed, which is 16,000 times more energy than the world uses per year in this day and age. Assuming a 25% efficient solar-pumped laser orbiting at 0.1 AU, the required circular collector area would 1400km in diameter. It’s inconceivable that a minor cult of some sort could muster the resources necessary for its construction. It would be a formidable weapon as well (you could vaporize anything within a radius of a few AU with a more focussed beam), so it is unlikely that other branches of society would permit the construction of such a device. Any propulsion system capable of accelerating large objects to singificant fractions of c is also a weapon of mass destruction. I can imagine that their deployment and use will be tightly controlled, even in very advanced societies which consume enormous amounts of energy. This makes it very difficult for a cult (whether such cults would exist in a highly rational advanced society is in itself questionable) to mount lasting colonisation efforts across interstellar distances.

Scott G, I am dubious of that first reference that you gave on Jan27. It starts by correctly pointing out that life can be explained as the congruence of natural forces, and as such we can submit its origin to investigation. At that point the reader should we waiting with baited breath, to find out how simple the writer estimates the first life form to be, but he doesn’t. Basically he just looks at how improbable the development of one new ribozyme is once a self-replicating mechanism of high fidelity was already in place. So he was actually investigating evolution after the first life-form was present. What’s that got to do with abiogenesis?

That second reference just effectively said “don’t be too much in awe of life or you will have difficulty analysing it”. That is a good message, but irrelevant as no-one here seems to have that problem!

“You are supposing that germs would not only remain viable in the near absolute zero temperatures so far from the sun, but that they would also be able to replicate and spread under those conditions. With all due respect, I find that preposterous.”

Wrapped, freeze dried, then warmed with water to moderate temperatures as it approaches nearer to a star. Not saying it happened, just that it is a serious idea worthy of study.

I feel that now is the time to put in a plug for the modern theory of evolution (modern synthesis). The idea that biological things can evolve slowly with time and gain additional functionality on the way has been with us for at least two and a half millennia. What’s new and scientific about the modern theory is that it is based on the solid foundation that no new biological function will arise except by dint of *natural selection* acting over genes that are transmitted with sufficiently high fidelity and provide a trait of sufficient importance to further reproductive success that enduring advantage may accrue.

My plea is that we never forget that Darwin inspired breakthrough or the reasons that we can’t apply it to abiogenesis without extraordinary conditions that we then need to explain.

Bob, it is important that you know that a bacterium coming close enough to a star to be warmed to the melting point of water would receive a lethal dose of uv light in just a few seconds. Hoyle came up with elaborate mechanisms to try to overcome this. The most effective of these was that if a very large proportions of an organisms organics could be charred to graphite without killing it, this just might create a shield for the remains of that organism. This doesn’t sound excessively promising, but work done by Hoyle convinced me that it cannot as yet be totally dismissed.

Life bearing but dormant interstellar grains might need to only get within this sphere to interact with one of the perhaps trillions of comets which ultimately may allow that life to replicate and seed the entire sphere in time.

“You are supposing that germs would not only remain viable in the near absolute zero temperatures so far from the sun, but that they would also be able to replicate and spread under those conditions. With all due respect, I find that preposterous.”

LJK replies:

Within our current experience, it may seem preposterous, but I would not be surprised if there are creatures which can survive and thrive in space. Especially if they were genetically created or artificially produced to live in the void.

Do not forget this little bugger which was found swimming in the reactor pools of nuclear power plants:

“Several bacteria of comparable radioresistance are now known, including some species of the genus Chroococcidiopsis (phylum cyanobacteria) and some species of Rubrobacter (phylum actinobacteria); among the archaea, the species Thermococcus gammatolerans shows comparable radioresistance.[5] Deinocuccus radiodurans also has a unique ability to repair damaged DNA. It isolates the damaged segments in a controlled area and repairs it. This bacteria can also repair many small fragments from an entire chromosome.[12]”

Deinococcus and others have perfected DNA repair most likely as an adaptation to desiccation, not radiation. Radiation resistance is an “unintended” side effect. Impressive, though.

However, repair needs biochemical activity. There is no biochemistry possible at cryogenic temperatures, including DNA repair. Extended periods at low temperatures and high radiation are thus particularly difficult for an organism to survive, much less thrive in.

As I said in my last post, creatures could be either genetically engineered or just plain artificially designed to survive and thrive in open space and other environments that most Earth life would consider harsh.

Would it be easier and quicker to genetically engineer humans to survive on any kind of world in our Sol system, or spend thousands of years trying to terraform a planet to suit our current selves – which will probably be radically changed by the time such a world is ready anyway.

Eniac, to me, the idea that elaborate DNA repair mechanism evolved for desiccation resistance always smacked of desperation. There are easier ways to protect, than relying on repair after the damage is done.

This is a curious assessment. Desiccation destroys DNA, so an elaborate repair mechanism is a natural response. It is certainly much more plausible than a response to radiation. There really aren’t a lot of habitats with high dose radiation in nature. Unless you want to count space, but that is where desperation enters the picture.

Eniac, have another look at how amazingly complicated those repair mechanisms are (look especially closely at those double strand breakages). Also note that low fidelity double strand end matching mechanisms would be useless (my implication being that it must have originally evolved to repair each breakage as it happened, not to put hundreds of breakages together once rehydrated). Then compare it to the more common expedient of surrounding the DNA in a protective material at the onset of drying.

When life first arrived on Earth, there would have been higher radiation levels than today. Perhaps there were a few high radiation areas that were worth the payoff of inhabiting, and then that DNA repair mechanisms was later put to alternate use. Or perhaps it evolved for a different reason entirely.

The notion of intelligence makes no sense without a broader view of computation, argues one of the world’s leading AI researchers

kfc 02/06/2012

One of the buzzwords in artificial intelligence research these days is ‘embodiment’, the idea that intelligence requires a body.

But in the last few years, a growing body researchers have begun to explore the possibility that this definition is too limited. Led by Rolf Pfeifer at the Artificial Intelligence Laboratory at the University of Zurich, Switzerland, these guys say that the notion of intelligence makes no sense outside of the environment in which it operates.

For them, the notion of embodiment must, of course, capture how the brain is embedded in a body but also how this body is embedded in the broader environment.

Today, Pfeifer and Matej Hoffmann, also at the University of Zurich, set out this thinking in a kind of manifesto for a new approach to AI. And their conclusion has far reaching consequences. They say it’s not just artificial intelligence that we need to redefine, but the nature of computing itself.

The paper takes the form of a number of case studies examining the nature of embodiment in various physical systems. For example, Pfeifer and Hoffmann look at the distribution of light-sensing cells within fly eyes.

Biologists have known for 20 years that these are not distributed evenly in the eye but are more densely packed towards the front of the eye than to the sides. What’s interesting is that this distribution compensates for the phenomenon of motion parallax.

When a fly is in constant forward motion, objects to the side move across its field of vision faster than those to the front. “This implies that under the condition of straight flight, the same motion detection circuitry can be employed for motion detection for the entire eye,” point out Pfeifer and Hoffmann.

That’s a significant advantage for the fly. With any other distribution of light sensitive cells, it would require much more complex motion detecting circuitry.

Instead, the particular distribution of cells simplifies the problem. In a sense, the morphology of the eye itself performs a computation. A few years a go, a team of AI researchers built a robot called Eyebot that exploited exactly this effect.

What’s important, however, is that the computation is the result of three factors: simple motion detection circuitry in the brain, the morphology or distribution of cells in the body and the nature of flight in a 3-dimensional universe.

Without any of these, the computation wouldn’t work and, indeed, wouldn’t make sense.

We’ve looked at examples of morphological computation on this blog in the past (here and here for example). And Pfeifer has been shouting from the roof tops for several years, with some success, about the role that shape and form play in biological computation.

But today he and Hoffman go even further. They say that various low level cognitive functions such as locomotion are clearly simple forms of computation involving the brain-body-environment triumvirate.

That’s why our definition of computation needs to be extended to include the influence of environment, they say.

For many simple actions, such as walking, these computations proceed more or less independently. These are ‘natural’ actions in the sense that they exploit the natural dynamics of the system.

But they also say it provides a platform on which more complex cognitive tasks can take place relatively easily. They think that systems emerge in the brain that can predict the outcome of these natural computations. That’s obviously useful for forward planning.

Pfeifer and Hoffmann’s idea is that more complex cognitive abilities emerge when these forward-planning mechanisms become decoupled from the system they are predicting.

That’s an interesting prediction that should lend itself to testing in the next few years.

But first, researchers will have to broaden the way they think not only about AI but also about the nature of computing itself.

In the famous words of Arthur C. Clarke, “Any sufficiently advanced technology is indistinguishable from magic.” This phrase is often quoted to express the idea that an alien civilization which may be thousands or millions of years older than us would have technology so far ahead of ours that to us it would appear to be “magic.”

Now, a variation of that thought has come from Canadian science fiction writer Karl Schroeder, who posits that ”any sufficiently advanced technology is indistinguishable from nature.” The reasoning is that if a civilization manages to exist that long, it would inevitably “go green” to such an extent that it would no longer leave any detectable waste products behind. Its artificial signatures would blend in with those of the natural universe, making it much more difficult to detect them by simply searching for artificial constructs versus natural ones.

The idea has been proposed as an explanation for why we haven’t found them yet, based on the premise that such advanced societies would have visited and colonized our entire galaxy by now (known as the Fermi Paradox). The question becomes more interesting in light of the fact that astronomers now estimate that there are billions of other planets in our galaxy alone. If a civilization reaches such a “balance with nature” as a natural progression, it may mean that traditional methods of searching for them, like SETI, will ultimately fail.

Of course, it is possible, perhaps even likely, that civilizations much older than us would have advanced far beyond radio technology anyway. SETI itself is based on the assumption that some of them may still be using that technology. Another branch of SETI is searching for light pulses such as intentional beacons as opposed to radio signals.

But even other alternate searches, such as SETT (Search for Extraterrestrial Technology), may not pan out either, if this new scenario is correct. SETT looks for things like the spectral signature of nuclear fission waste being dumped into a star, or leaking tritium from alien fusion powerplants.

The Search for Extraterrestrial Intelligence (SETI) has a low probability of success, but it would have a high impact if successful. Physicists Paul Davies and Robert Wagner of Arizona State University argued last year that it makes sense to widen the search to scour the Moon for possible alien artifacts. At Penn State, researchers propose the same type of searchsearch for Mars. To date, SETI has been dominated by the paradigm of seeking deliberately beamed radio messages.

The ASU team argued that Alien civilizations may have sent probes to our region of the galaxy, and that any mission to the solar system would probably have occurred a very long time ago. The lunar environment could preserve artifacts for millions of years due to the absence of erosion and plate tectonics.

Indirect evidence for extraterrestrial intelligence could come from any incontrovertible signatures of non-human Alien technology. Existing searchable databases from astronomy, biology, earth and planetary sciences all offer low-cost opportunities to seek a footprint of extraterrestrial technology.

Davies and Wagner reason that the rapidly-expanding database of the photographic mapping of the Moon’s surface by the Lunar Reconnaissance Orbiter (LRO) to 0.5 m resolution offers an ideal opportunity to search for ancient artifacts and has mapped a quarter of the moon’s surface since mid-2009.

Among the LRO images, scientists have spotted the Apollo landing sites as well as all of the Nasa and Soviet unmanned probes, some of which were revealed only by their odd-looking shadows.

Nasa has made more than 340,000 LRO images public, but that figure is expected to reach one million by the time the orbiting probe has mapped the whole lunar surface. “From these numbers, it is obvious that a manual search by a small team is hopeless,” the scientists write.

The seismometer on Nasa’s Apollo 12 mission detected only one impact per month from roughly grapefruit-sized meteorites within a 350km radius. According to Davies and Wagner, it could take hundreds of millions of years for an object tens of metres across to be buried by lunar soil and dust kicked up by these impacts. Software can search for strange-looking features, such as the sharp lines of solar panels, or the dust-covered contours of quarries or domed buildings. These might be visible millions of years after they were built.

Systematic scrutiny of the LRO photographic images is being routinely conducted for planetary science purposes, and this program could be expanded and outsourced at little extra cost to accommodate SETI goals, after the fashion of the SETI@home and Galaxy Zoo crowd-sourcing projects. Hundreds of thousands of pictures of the moon will be examined for telltale signs that aliens once visited our cosmic neighbourhood if plans go ahead. Online volunteers could be set task of spotting alien technology, evidence of mining and rubbish heaps in moon images.

Elswhere, two researchers at Penn State, are asking “why have we never found evidence of other civilizations in Solar System?” The team is approached the problem mathematically, which shows that we have not looked in enough places to ensure that no extraterrestrial artifacts exist in our solar system.

Even without actual contact, like us, other civilizations could be sending unpiloted probes to quietly peek at our civilization. These probes, like ours, would be small and might be hidden in a variety of places. In the asteroid belt they would probably go unnoticed, especially if these nonterrestrial objects are only 3 to 33 feet in size, weighing little more than a ton similar to our Voyager craft.

“Extraterrestrial artifacts may exist in the solar system without our knowledge simply because we have not yet searched sufficiently,” said Haqq-Misra and Kopparapu. “Few if any of the attempts would be capable of detecting a 1 to 10 meter (3 to 33 foot) probe.”

Haqq-Misra and Kopparapu use a probabilistic method to determine if we have looked closely enough anywhere in the solar system to definitively say there are no nonterrestrial objects here. The analysis is based on answering the question, how sure can we be that we should have already found any nonterrestrial objects lurking in the solar system.

They view the solar system as a fixed volume and figure out the percentages of that volume that would need to be thoroughly searched using a discovery capability small enough to detect these probes, assuming that the probes are not consciously camouflaged. The researchers note that most searches to date have not been fine enough to locate such small probes or to totally rule out anywhere.

After taking into account a variety of potential biases, such as “the universe is teeming with life” or “life is rare,” the team developed an equation that can be applied to a portion of the volume of the solar system and determine whether sufficient searching has been done to ensure that we can say there are no nonterrestrial objects within that volume.

“The surface of the Earth is one of the few places in the solar system that has been almost completely examined at a spatial resolution of less than 3 feet,” said Haqq-Misra and Kopparapu.

But even as humans have spread across the solid surfaces of the Earth, there are still caves, jungles and deserts as well as the ocean floor and subsurface areas that have not been explored. Even with this, the Earth does have a high confidence that no nonterrestrial artifacts exist.

The moon and Mars have been searched to a small extent. An ongoing mapping project, the Lunar Reconnaissance Orbiter, is looking at the moon at a resolution of about 20 inches, so we may eventually be able to determine if there are no nonterrestrial objects on the moon. The researchers caution that surface maps may not be sufficient to distinguish between a space probe and a rock.

The surface of Mars is still mostly unsurveyed and the researchers’ confidence in the probability of no nonterrestrial artifacts is low. Similarly, locations like the Earth-moon Lagrange points, the asteroid belt and the Kuiper belt might also shelter extra solar system probes, but the vast majority of the solar system’s volume is uninvestigated.

“Searches to date of the solar system are sufficiently incomplete that we cannot rule out the possibility that nonterrestrial artifacts are present and may even be observing us,” said Haqq-Misra and Kopparapu. They add that “the completeness of our search for nonterrestrial objects will inevitably increase as we continue to explore the moon, Mars and other nearby regions of space.”

The infrared images of Mars at the top of the page show both reflected sunlight and heat radiation. The left one is taken in the near-IR and Mars looks a lot like the eye would see it, with the south pole clearly visible as well as continents. The thermal (heat) image to the right is taken in the so-called M band and clearly shows cold and warm regions on Mars.

Unlike astronomy, archaeology seems a bit less friendly to its amateur counterparts. They would probably have a better chance of finding an object made by beings from another world, and an even more likely chance of reporting it.

Of course they also have an even greater chance of misinterpreting the item or going the ol’ hoax route.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last nine years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

On Comments

Centauri Dreams publishes selected comments on the articles under discussion here. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. A fuller statement of the policy can be viewed on the Administrative page.